Communication devices or user terminals, such as user equipment (UE), a mobile station (MS), a cellular phone, a personal digital assistant (PDA) or a personal computer (PC), or any other equipment operable according to a suitable network protocol, such as a wireless applications protocol (WAP) or a hypertext transfer protocol (HTTP), may be used for accessing a communication system. A communication system can be seen as a facility that enables communication sessions between two or more entities such as communication devices and/or other nodes associated with the communication system. Wireless communication systems may provide mobility for users thereof. Wireless communication systems may comprise cellular systems, e.g. global system for mobile communications (GSM), general packet radio service (GPRS) and universal mobile telecommunications system (UMTS), and non-cellular systems, e.g. wireless local area network (WLAN) and Bluetooth. Transfer techniques may comprise, for example, time division multiple access (TDMA), frequency division multiple access (FDMA), code division multiple access (CDMA) and wideband CDMA (WCDMA). Wireless communication systems may establish communication sessions also with other communication systems, such as fixed line communication systems, e.g. a public switched telephone network (PSTN) or with packet switched data networks, e.g. Internet Protocol (IP) networks.
A communication device may be used for tasks such as for making and receiving phone calls, for receiving and sending data from and to the network and for experiencing multimedia content or otherwise using multimedia services. A communication device may include an antenna for wirelessly receiving and transmitting radio frequency (RF) signals from and to transceiver network elements of a communication network. A communication device may also be provided with a display, camera means, speaker means, and so on. The operation of a communication device may be controlled by means of an appropriate user interface such as control buttons, voice commands and so on. Furthermore, a communication device is provided with a processor entity and a memory means.
In a mobile communication device, such as a mobile station or user equipment, electrical memory means have typically been provided by means of semiconductor technology. Such electrical memory means are not sensitive for external magnetic fields. They can be effectively shielded from electrical interferences since they are physically small devices. A physical size of a memory circuit used in mobile phones is typically smaller than 1 cm by 1 cm, height being a couple of millimeters.
Demands for memory capacity are continuously increasing due to expanding amount and size of applications and user data transferred and stored by means of mobile communication devices. Hard disks might provide additional or larger memory capacity for storing and processing applications and data for mobile user equipment.
Hard disks, or fixed disks, typically store data in tracks in a rotating disk and use a reading and writing head(s) for handling the data. In this specification, the reading/writing head is called simply a reading head in order to simplify the terminology. However, this term may comprise both the reading and the writing operation in the hard disk. This same reading and writing principle may also be used in optical disks, e.g. a compact disk (CD), a digital versatile disk (DVD), and in magneto-optical disks, e.g. a mini disk (MD).
In communication devices, RF signals may generate strong electromagnetic fields when the RF signals propagate through transmitter or receiver chains. A reading head of a hard disk may employ a magnetic field, which is applied to a coil of the reading head. External electromagnetic fields, or RF signals, may cause problems to the reading head controlling of reading/writing data. Furthermore, external electromagnetic fields may corrupt the data between a hard disk and a mobile terminal. As a result the hard disk may not function correctly. For example, the reading head may be positioned in an incorrect track resulting in reading or writing errors.
A hard disk may be protected against external electromagnetic fields by improving a shielding surrounding the hard disk in a communication device. The shielding may, however, increase cost and weight of the user equipment. The shielding may also not guarantee that no electromagnetic waves propagate to the hard disk.
Another solution could be protecting the hard disk by minimizing sources of electromagnetic waves. This would require adequately shielding the RF signals within RF modules transmitting and receiving the RF signals. However, this may not always be possible due to interconnections on the PWB (printed wired board) and a non-perfect ground plane. Also, an electromagnetic field generated by the transmission of the radio communication signal from an antenna can harm the hard disk operation.
U.S. Pat. No. 6,023,390 describes bias force disturbance and runout disturbance compensation in an actuator of a magnetic disk drive by means of an algorithm. Bias force disturbances are caused by an elastic character of a flexible printed circuit cable connected to the actuator. Runout disturbances are caused by transversal irregularities of the disk, which may arise when the center of the disk is not precisely aligned with the spindle motor axle, or when the disk is defectively mounted.
There is a need for improved protection of hard disks and other memory devices against external electromagnetic fields. This may lead to a solution allowing or facilitating a use of various memory devices, for example hard disks, in communication devices transmitting and receiving RF signals. In particular, improved protection may be useful in mobile user equipment where size and weight of the equipment may be significant.